One of the central questions of cellular and molecular immunology concerns the specific events which occur as T cells develop within the thymus, a process thought to be intimately involved in shaping the peripheral T cell repertoire of an individual. We propose to create transgenic mice bearing genes encoding subunits of a functional T cell receptor and to styd the effects of the foreign genes upon the developing T cell repertorie. The thymus is believed to be responsible for "educationg" developing thymocytes with respect to immunologic self tolerance and major histocompatibility complex (MHC) restriction, such that mature T cells wil not react to self MHC alone, but are activated by antigen in association with self MHC. Thymocytes autoreactive against self Ia antigen appear to be abundant in the maturing thymus, and the developmental fate of such cells is unclear. Autoreactive thymocytes may be deleted prior to exiting the thymus as a step toward self tolerance, or may be expanded and ultimately give rise to a significant portion of the mature T cell repertoire. We will use recombinant DNA techniques to clone the rearranged, functional and beta T cell receptor (TCR) genes from the genomic DNA of an autoreactive T cell hybridoma (E8.A1) which is specific for A-Ak. These genes, containing both transcriptional promotor and coding sequences, will be introduced into the germline of mice, and the transgenes genetically crossed into the H-2k haplotype. These transgenic mice and their progeny should express an autoreactive TCR in a high proportion their developing thymocytes. Using transgene-specific nucleic acid probes and an anti-idiotypic antibody, these mice will be used to answer the following questions: 1) Do these mice survive, and do they develop autoimmune disease? 2) What fractio of thymocytes express the transgenic TCR, and are these autoreactive thymocytes permitted to exit the thymus? 3) Does expression of the transgenic TCR during development alter the mature T cell repertoire of the animal?